Sandmeier disclosed a removable inner sole for footwear in his U.S. Pat. No. 4,215,492 which includes an interior chamber for the forced flow of air unobstructed and uninterruptedly between the heel and toe portions thereof and through inlet and outlet openings.
The inner sole comprises two overlaid members having a U-shaped spacer interposed the sole members along the marginal edges of the heel portion and having a plurality of protrusions integrally formed on the upper member near the toe portions.
However, such a conventional insole still has the following drawbacks:
1. For making a low cost footwear such as a slipper, the two-member insole will require a higher production cost, especially when bonding the spacer between the two members.
2. The plural protrusions formed on the insole are only disposed on the front portion near the toe portions and may not exert a better massage effect by such plural protrusions.
3. If the protrusions are widely spread to fully distribute on the upper member including the heel portion, the heel portion will be increased its height to discomfort a wearer's heel. Accordingly, the massage effect by Sandmeier's device is quite limited.
The present inventor has found the drawbacks of a conventional inner sole and invented the present single-layer ventilating and massaging insole.